1. Field of the Invention
The present invention relates to a cosmetic preparation comprising 1,2-hexanediol.
2. Discussion of Background Information
The desire to appear beautiful and attractive is naturally rooted in man. Even if the beauty ideal has undergone changes over the course of time, the desire for a flawless outward appearance has always been the aim of human beings. The condition and the appearance of the skin is a significant part of a beautiful and attractive outward appearance.
In order for the skin to completely fulfill its biological functions it requires regular cleansing and care. Cleansing the skin thereby serves to remove dirt, perspiration and remains of dead skin particles which form an ideal breeding ground for pathogens and parasites of all types. Skin care products serve mostly to moisturize and regrease the skin. Active ingredients are often added to them which regenerate the skin and, for example, are intended to prevent and reduce its premature ageing (e.g., the appearance of fine lines and wrinkles).
Skin care products are usually composed of emulsions. Emulsions are generally understood as meaning heterogeneous systems which consist of two liquids which are immiscible or of only limited miscibility and which are usually referred to as phases and in which one of the two liquids is dispersed in the form of very fine droplets in the other liquid. Outwardly and viewed with the naked eye, emulsions appear homogeneous.
If the two liquids are water and oil and oil droplets are present in finely dispersed form in water, this is an oil-in-water emulsion (O/W emulsion, e.g., milk). The basic character of an O/W emulsion is defined by the water. In the case of a water-in-oil emulsion (W/O emulsion, e.g., butter), the principle is reversed, the basic character here being determined by the oil.
In order to keep emulsions stable over a prolonged period and to prevent separation of the phases, so-called emulsifiers are added to the emulsions. Emulsifiers as a rule are molecules with a polar, hydrophilic structural element and a nonpolar, lipophilic structural element. In the late 1940s a system was developed that was designed to facilitate the selection of emulsifiers. Each emulsifier was assigned a so-called HLB value (a dimensionless number between 0 and 20) that states whether a preferred water-solubility or oil-solubility is present. Numbers below 9 characterize oil-soluble, hydrophobic emulsifiers, numbers over 10, those that are water-soluble, hydrophilic.
In the production of an emulsion, the aqueous phase is combined with the lipid phase (oil phase) while being stirred, whereby the droplets of the internal phase of the emulsion have to be reduced to below 10 μm in size so that the emulsion becomes stable.
In the production of O/W emulsions with hydrophilic emulsifiers (emulsifiers with an HLB value of greater than/equal to 10) the problem often occurs that with the use of primarily moderately polar to polar lipids in the oil phase (i.e., lipids with a interfacial tension toward water of less than about 30 mN/m) an undesirable inversion of phases can occur. Furthermore, O/W emulsions of this type have a tendency towards phase inversion during storage, i.e., the preparations are often not very stable during storage.
It would be advantageous to have available an O/W emulsion with hydrophilic emulsifiers and a method for producing an O/W emulsion with hydrophilic emulsifiers with a substantially reduced phase inversion tendency during production and/or storage.